Get rid of old style backquoting

* lisp/ox-texinfo.el (org-texinfo-export-to-texinfo): Use new style
backquoting.
(org-texinfo-export-to-info): Use new style backquoting.

Thanks to Mehul Sanghvi for the patch.

lisp/ox-texinfo.el

@@ -1710,7 +1710,7 @@ file-local settings.
 Return output file's name."
   (interactive)
   (let ((outfile (org-export-output-file-name ".texi" subtreep))
-	(org-export-coding-system ',org-texinfo-coding-system))
+	(org-export-coding-system `,org-texinfo-coding-system))
     (org-export-to-file 'texinfo outfile
       async subtreep visible-only body-only ext-plist)))
 
@@ -1747,7 +1747,7 @@ directory.
 Return INFO file's name."
   (interactive)
   (let ((outfile (org-export-output-file-name ".texi" subtreep))
-	(org-export-coding-system ',org-texinfo-coding-system))
+	(org-export-coding-system `,org-texinfo-coding-system))
     (org-export-to-file 'texinfo outfile
       async subtreep visible-only body-only ext-plist
       (lambda (file) (org-texinfo-compile file)))))